1. Technical Field
Embodiments of this disclosure generally relate to a fixing device to fix an unfixed toner image onto a recording medium by electromagnetic induction heating, and to an electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine having two or more of copying, printing, and facsimile capabilities, incorporating the fixing device.
2. Related Art
Image forming apparatuses may incorporate a fixing device employing an electromagnetic induction heating method to reduce startup time of the image forming apparatuses, thereby enhancing energy efficiency. Such a fixing device employing the electromagnetic induction heating method includes, e.g., a heating roller serving as a heat generator, a fixing roller, an endless fixing belt stretched over the heating roller and the fixing roller, an induction heater facing the heating roller via the fixing belt, and a pressing roller to contact the fixing roller via the fixing belt. The induction heater includes, e.g., an excitation coil wound in a longitudinal direction of the induction heater, cores to direct alternating magnetic flux arising from the excitation coil to the heat generator, and a holder (or coil guide) to hold the excitation coil and the cores.
The induction heater faces and heats the fixing belt. The heated fixing belt heats and fixes a toner image formed on a recording medium conveyed between the fixing roller and the pressing roller. Specifically, a high-frequency alternating current supplied to the excitation coil forms an alternating magnetic field around the excitation coil, which generates eddy currents on a surface of the heating roller. When the eddy currents are generated around the heating roller serving as a heat generator, the electrical resistance of the heating roller leads to Joule heating of the heating roller, thereby heating the fixing belt stretched over the heating roller.
In such a fixing device employing the electromagnetic induction heating method, the heat generator is directly heated by electromagnetic induction. Accordingly, compared to a typical fixing device using a halogen heater, the fixing device employing the electromagnetic induction heating method has a higher heat-exchange efficiency and therefore the surface temperature of the fixing belt can be increased to a desired fixing temperature more efficiently, that is, with less energy and a shorter startup time.
Toner includes wax to enhance fixing performance at a low temperature, and to facilitate separation of recording media from a fixing member (fixing belt or fixing roller) and a pressing member (pressing roller or pressing belt). When such toner including wax is used for a fixing operation employing the induction heating method, the wax may cause fixing failures, e.g., the wax may adhere to a recording medium during fixing of an image formed on the recording medium. Specifically, the wax is evaporated when the toner is heated in the fixing nip. The evaporated wax floats and moves by rotation of the fixing member, and consequently adheres to the holder (or coil guide) of the induction heater that is disposed facing the fixing member, particularly to a surface that faces the fixing member. As the wax adhering to the holder accumulates, it eventually fills a small gap between the induction heater and the fixing member, and some of the wax adheres to the fixing member. The wax adhering to the fixing member is fused again and adheres to the recording medium in the fixing nip, thereby causing a fixing failure in that the wax adheres to the recording medium during fixing of the image formed on the recording medium.
As one approach to such fixing failure, JP-2009-288578-A provides a passage for drainage on a surface of an induction heater facing the fixing member to drain off any wax adhering to the surface. Yet the wax may still accumulate without being drained, depending on how the induction heater is oriented. Moreover, the drainage passage is provided in a holder (or coil guide) made of resin, and because the resin has good heat resistance, the accumulated wax is easily fused again upon absorbing heat from the fixing member. Consequently, the wax adheres to a recording medium during fixing of an image formed on the recording medium.